1. Field of Invention
The present invention relates to a network probe. More particularly, the present invention relates to a probe of two-way optical component network analyzer.
2. Description of Related Art
In general, a conventional microwave network analyzer is capable of measuring the S-parameters, the reflection coefficients, the transmission coefficients and the frequency responses of a component. Hewlett Packard has extended application of the analyzer to measuring the S-parameters of optical-electronic elements such as light transmitters and light receivers. However, the analyzer is only capable of unidirectional measurement of the S-parameters. Although unidirectional measurement of S-parameters is sufficient for measuring light transmitters or light receivers, measurement of optical elements such as fiber ring loop resonator or fiber grating becomes very inconvenient. In order to measure all four S-parameters of a two-port optical element, the analyzer needs to be dismantled after a measurement in a first direction and reassembled for a second measurement in the opposite direction.
Since the design of an optical system depends on obtaining correct optical parameters, precise measurement of optical parameters in both directions is very important.
In 1985, Donald R. Bowling et al has proposed a multi-channel instrument for measuring dispersion parameters in U.S. Pat. No. 4,497,030. The measuring instrument is actually the combination of a power distributor with an automatic network analyzer produced by Hewlett Packard (HP8409A). The instrument utilizes a co-axial exchange network to adjust the radio frequency (RF) when different channels are selectively measured. Although the method in that invention is not included in the scope of this invention, they can be combined to form a bi-directional measuring instrument for the parameters of a multi-port optical element.
In 1997, Atsushi Ishihara has proposed a method of synchronizing network measurement element in U.S. Pat. No. 5,646,536. The object of the invention is to provide a method of synchronizing multi-channel bi-directional measurement. However, externally mounted measuring probe or something similar to the bi-directional optical probe of this invention is excluded.
In 1994, Paul S. Weiss and Stephan J. Stranick has proposed a method of sending testing signals from a microwave sweep oscillator to a test sample in U.S. Pat. No. 5,281,814. Signals reflecting from the test sample are delivered to a network analyzer, and then the signals are analyzed to obtain a frequency response. Frequency adjustment is controlled by the microwave sweep oscillator. The invention is a new type of probe that enables a network analyzer to improve the resolution of a scanning tunnel microscope. Yet, the probe has a function, structure and application entirely different from the bidirectional probe proposed in this invention.
In 1990, David Curtls and Elizabeth E. Ames has proposed a method of obtaining the dispersion parameters of an optical element through a vector network analyzer in xe2x80x9cTransaction on Microwave Theory and Techniquesxe2x80x9d, IEEE vol. 38, issue 5, pg. 552xcx9c559. The network analyzer sends out an electrical signal to an optical transmitter, and then the optical transmitter emits an optical signal to a test element. Response signals from the test element are transferred to an optical receiver. Optical signals to the optical receiver are converted back to electrical signals and sent to the network analyzer to obtain the S-parameters. The main drawback of the method is the use of directional coupler. To measure the optical parameters in the opposite direction, the optical element must be remounted leading to possible alignment errors.
Accordingly, one object of the present invention is to provide a bi-directional measuring probe and method of measurement capable of eliminating human errors.
A second object of this invention is to provide the probe of a bi-directional analyzer for measuring the S-parameters of an optical component or network element. All the optical parameters needed are obtained in a single setting without the need to rotate the optical element. In addition, the resulting parameters are more accurate.
The testing system for measuring optical parameters includes a HP network analyzer and the specially designed bidirectional probe of this invention. Using the testing system, testing time is shortened because there is no need to reset the optical element again in the opposite direction. In addition, accurate readings for the optical parameters are obtained because human errors due to resetting are prevented.
One major aspect of the testing system is its bi-directionality of measurement. The system is capable of obtaining the frequency response of S-parameters of an optical element at various frequencies quickly. Moreover, the probe of this invention can be easily incorporated with various microwave network-analyzing instruments in the market for obtaining optical parameters S11, S12, S21 and S22.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a bi-directional probe for analyzing an optical component or network. The probe includes an electrical circulator, an optical transmitter, an optical receiver, and an optical circulator. The electrical circulator is connected to the optical transmitter by an electrical cable. The electrical circulator transmits incoming electrical signals from the network analyzer to the optical transmitter where the electrical signals are converted to optical signals and directed to the optical element to be tested. The optical receiver picks up return signals from the optical element and converts the optical signals into electrical signals. The electrical signals from the optical receiver pass through the electrical circulator and return to the network analyzer. Through the electrical circulator, incoming and outgoing electrical signal follows separate pathways so that unnecessary electrical interference is avoided. The optical transmitter is connected to the optical circulator by an optical fiber. The optical transmitter converts electrical signals into optical signals and then directs the optical signals to the optical circulator. The optical transmitter also picks up incoming optical signals and converts the optical signals into electrical signals. The electrical signals from the optical transmitters are transmitted to the optical circulator. The optical circulator is connected to the optical receiver by an optical fiber. The optical circulator is capable of separating incoming light wave from reflected light wave without optical interference so that forward light signals are directed to the optical element while reflected light signals are returned to the optical receiver. The optical receiver is connected to the electrical circulator by an electrical cable. The reflected optical signals are converted into electrical signals by the optical receiver, and then the electrical signals are transmitted back to the network analyzer via the electrical cable and the electrical circulator.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.